1. Field of the Invention
The present invention relates to photo nanoimprint lithography of transferring a surface geometry of a mold onto a surface of a substrate.
2. Background Art
Network technology, software technology and device technology are needed to further develop due to the tendency of recent advances in information technology. To a semiconductor integrated circuit, in particular, such a high technology is required that the circuit is further refined and integrated, consequently is operated at a higher speed and is operated with low power consumption. Currently, photolithography is shifted from KrF laser lithography having the minimum line width of 130 nm to ArF laser lithography having higher resolution. However, the minimum line width of ArF laser lithography is 100 nm at a mass production level, whereas a device having the minimum line width of 45 nm is starting to be manufactured in the year 2007. In such a situation, technologies expected as a further refining technique include F2 laser lithography, extreme ultraviolet lithography, electron beam reduced projection lithography and X-rays lithography. However, as a finer patterning technology progresses, an initial cost of the exposure device itself exponentially increases, and besides there is a problem that the price of a mask for obtaining the same level of resolution as that of the wavelength of a used light rapidly rises.
As technology for coping with the problem, there is imprint lithography of forming a fine pattern. Imprint lithography is technology that transfers a predetermined pattern onto a substrate by pressing a mold having the same asperities as a pattern which is desired to be formed on the substrate against a surface of the substrate or a resin on the substrate, and then by releasing the mold, and that can simply and easily form a fine structure having a width between the asperities of 50 nm or less, though being inexpensive. For this reason, it has been investigated to apply the imprint technique to fields of forming a recording bit on a high-capacity recording medium, forming a pattern of a semiconductor integrated circuit, or the like.
Nanoimprint lithography is roughly classified into two types according to a material to be transferred therein. One is thermal nanoimprint lithography of heating the material to be transferred therein, plastically deforming the material with the mold and cooling the material to form a pattern. The other is photo-nanoimprint lithography of applying liquid photo-curable resist to substrate at room temperature, pressing an optically transparent mold to the resist, irradiating the resist with a light to cure the resist on the substrate, and consequently forming the pattern. In particular, the photo-nanoimprint lithography can form patterns at room temperature, accordingly hardly causes distortion due to the difference in linear expansion coefficient caused by heat between the substrate and the mold, can form a pattern of high precision, and receives attention as an alternative technique of a lithographic technology for a semiconductor or the like.
In a transferred pattern with fine asperities being formed when a photo-curable resist is cured, a base layer of the photo-curable resist is formed in its recess part. In order to transfer the fine asperity pattern onto the substrate, the base layer is usually removed by a dry etching technique, a wet etching technique or the like. In order to transfer the fine asperity pattern onto the substrate with high accuracy, it is required to uniformize a film thickness of the base layer and thin a film of the base layer on the surface to be transferred onto.
Conventionally, a countermeasure of increasing a pressing force in pressing the mold or the like has been taken as means for thinning the film of the base layer of the photo-curable resist, but has had a problem of occasionally causing a fracture of the mold because a large force is applied to the mold when the pressure is increased.
In order to solve such a problem, JP Patent Publication (Kokai) No. 2004-304097A proposes the following transfer method. The transfer method specifically provides a polymer film for controlling the reaction of a photo-curable resist on the surface of the projecting parts of the mold. The polymer film for controlling the reaction of photo-curable resist is a polymer having a function of blocking or absorbing a light having a wavelength of a light source to be used for a photo-curing reaction. When the mold having this polymer film for controlling the reaction of photo-curable resist is used in a transferring operation, the photo-curing reaction does not proceed in the photo-curable resist right under the polymer film for controlling the reaction of photo-curable resist, so that the transferred film free from the base layer can be formed by cleaning an uncured photo-curable resist.
In addition, JP Patent Publication (Kohyo) No. 2005-533393A proposes a method of applying a photo-curable resist with the use of an ink-jet technique. The method with the use of the ink-jet technique can specify positions of the droplets of the resist and discretely apply the resist onto the substrate, and accordingly can control the distribution of film thickness, because the droplets are uniformly spread when the mold has been pressed onto the droplets.